BroadcastReceiver

在Android中，Broadcast是一种广泛运用的在应用程序之间传输信息的机制。而BroadcastReceiver是对发送出来的 Broadcast进行过滤接受并响应的一类组件。由于BroadcastReceiver本质上也是一种监听器，一次实现BroadcastReceiver只要重写其onReceive(Context context, Intent intent) 方法就可以了。
实现方法：
1.注册BroadcastReceiver
2.发送Broadcast消息
3.重写onReceive（）方法

　注册BroadcastReceiver有两种方式:静态注册方式和动态注册方式。下面依次介绍
　静态注册方法:
　是在在AndroidManifest.xml中用标签生命注册，并在标签内用标签设置过滤器
　

 <receiver
            android:name=".MyReceiver"
            android:enabled="true"
            android:exported="true">
            <intent-filter android:priority="9">
                <action android:name="org.crazyit.learnbroadcastreceive.intent.action.MyReceiver" />
            </intent-filter>
 </receiver>

会在Android Studio自动完成。

动态注册方法：

 //为了防止重复注册多个BroadcastReceivr
                if(receiver==null){
                    receiver=new MyReceiver();
                    registerReceiver(receiver,new IntentFilter(MyReceiver.ACTION));
                }

卸载：

 if(receiver!=null){
                     unregisterReceiver(receiver);
                    receiver=null;
                }

　
2.发送Broadcast消息

 Intent intent=new Intent(MyReceiver.ACTION);
                //通过Intent携带一些数据
                intent.putExtra("data","jikexueyuan");
                //sendBroadcast(intent);
                //发送有序消息，可以被优先级高的
//BroadcastReceiver接收到消息后阻断，
                //此时优先级低的BroadcastReceiver不能继续受到消息
                sendOrderedBroadcast(intent,null);

3.重写onReceive（）方法
我们可以设置接收器不同的优先级，当发送无序消息时，逻辑上所有接收器是同时接收到消息的，缺点是接受者不能将处理过的消息发送给下一个接受者。而有序消息是按预先声明的优先级一次接收的。如果优先级A>B,则先A接收到消息，A再把消息（可以处理）传给B，也可以A直接把消息阻断，不允许B接收。
接收器MyReceiver接收消息，并阻断：

  public void onReceive(Context context, Intent intent) {
        System.out.println("接收到了消息,消息的内容是:"+intent.getStringExtra("data"));
        //用来中断优先级排在他后面的接收器接收到消息，不过前提是发送的消息是有序的，即sendOrderedBroadcast;
        abortBroadcast();

    }

此时优先级较低的MyReceiver1将不能接收到任何消息
接收器MyReceiver接收消息，并把消息处理后传递给MyReceiver1

 public void onReceive(Context context, Intent intent) {
        System.out.println("接收到了消息,消息的内容是:"+intent.getStringExtra("data"));
        //用来中断优先级排在他后面的接收器接收到消息，不过前提是发送的消息是有序的，即sendOrderedBroadcast;
        //abortBroadcast();
        Bundle bundle=new Bundle();
        bundle.putString("first","我是MyReceiver传送的消息");
        //将 bundle放入结果中
        setResultExtras(bundle);

    }

此时MyReceiver1将接收到消息：

  public void onReceive(Context context, Intent intent) {
        System.out.println("MyReceive1接收到了消息");
        Bundle b=getResultExtras(true);
        //解析第一个BroadcastReceiver传递过来key为first的消息
        String string=b.getString("first");
        Toast.makeText(context,"第二个receiver接收到的消息是：第一个receiver传过来的消息"+
                string+"和MainActivity传给第一个Receiver的消息："+intent.getStringExtra("data"),Toast.LENGTH_SHORT).show();

    }

最后附上总的代码：
MainActivity.java

import android.content.Intent;
import android.content.IntentFilter;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity implements View.OnClickListener {
     Button btnSendMsg;
     Button btnReg,btnUnreg;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        btnSendMsg=(Button) findViewById(R.id.btnSendMsg);
        btnReg=(Button) findViewById(R.id.btnReg);
        btnUnreg=(Button) findViewById(R.id.btnUnreg);
        btnSendMsg.setOnClickListener(this);
        btnReg.setOnClickListener(this);
        btnUnreg.setOnClickListener(this);

    }

    @Override
    public void onClick(View view) {
        switch (view.getId()){
            case R.id.btnSendMsg:
                /* 通过Manifest文件进行注册时
                Intent intent=new Intent(this,MyReceiver.class);
                //通过Intent携带一些数据
                intent.putExtra("data","jikexueyuan");
                sendBroadcast(intent);*/
                /*

                * 通过下面java代码进行注册时*/
                Intent intent=new Intent(MyReceiver.ACTION);
                //通过Intent携带一些数据
                intent.putExtra("data","jikexueyuan");
                //sendBroadcast(intent);
                //发送有序消息，可以被优先级高的BroadcastReceiver接收到消息后阻断，
                // 优先级低的BroadcastReceiver不能继续受到消息
                sendOrderedBroadcast(intent,null);
                break;
            //在java代码中注册和注销接收器更加的灵活啊，可以用在不需要时刻接收消息的情况下
            case R.id.btnReg:
                //为了防止重复注册多个BroadcastReceivr
                if(receiver==null){
                    receiver=new MyReceiver();
                    registerReceiver(receiver,new IntentFilter(MyReceiver.ACTION));
                }
                break;
            case R.id.btnUnreg:
                if(receiver!=null){
                     unregisterReceiver(receiver);
                    receiver=null;
                }
                break;

        }
    }

    private MyReceiver receiver=null;
}

MyReceiver.java

//程序发送有序Broadcast，MainActivity传送消息A给 MyReceiver， MyReceiver继续传送消息B给MyReceiver1
//此消息B可以是消息A，也可以不是
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;

public class MyReceiver extends BroadcastReceiver {
    public static final String ACTION="org.crazyit.learnbroadcastreceive.intent.action.MyReceiver";
    public MyReceiver() {
    }

    @Override
    public void onReceive(Context context, Intent intent) {
        System.out.println("接收到了消息,消息的内容是:"+intent.getStringExtra("data"));
        //用来中断优先级排在他后面的接收器接收到消息，不过前提是发送的消息是有序的，即sendOrderedBroadcast;
        //abortBroadcast();
        Bundle bundle=new Bundle();
        bundle.putString("first","我是MyReceiver传送的消息");
        //将 bundle放入结果中
        setResultExtras(bundle);

    }
}

MyReceiver1.java

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.widget.Toast;

public class MyReceiver1 extends BroadcastReceiver {
    public MyReceiver1() {
    }

    @Override
    public void onReceive(Context context, Intent intent) {
        System.out.println("MyReceive1接收到了消息");
        Bundle b=getResultExtras(true);
        //解析第一个BroadcastReceiver传递过来key为first的消息
        String string=b.getString("first");
        Toast.makeText(context,"第二个receiver接收到的消息是：第一个receiver传过来的消息"+
                string+"和MainActivity传给第一个Receiver的消息："+intent.getStringExtra("data"),Toast.LENGTH_SHORT).show();

    }
}

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="org.crazyit.learnbroadcastreceive">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <!-- 这段代码也可以注释掉，然后在java程序里面实现动态注册与注销BroadcastReceive -->
        <!-- <receiver -->
        <!-- android:name=".MyReceiver" -->
        <!-- android:enabled="true" -->
        <!-- android:exported="true"></receiver> -->
        <receiver
            android:name=".MyReceiver"
            android:enabled="true"
            android:exported="true">
            <intent-filter android:priority="9">
                <action android:name="org.crazyit.learnbroadcastreceive.intent.action.MyReceiver" />
            </intent-filter>
        </receiver>

        <receiver
            android:name=".MyReceiver1"
            android:enabled="true"
            android:exported="true">
            <intent-filter android:priority="8">
                <action android:name="org.crazyit.learnbroadcastreceive.intent.action.MyReceiver" />
            </intent-filter>
        </receiver>
    </application>

</manifest>

BroadcasrReceiver还可以接收系统广播，例如

<receiver android:name=".BootBroadcasrReceiver" >
    <intent-filter>
        <!-- 接受系统开机广播 -->
        <action android:name="android.intent.action.BOOT_COMPLETED"/>
        <category android:name="android.intent.category.HOME"/>
    </intent-filter>
</receiver>

然后只要在onReceiver函数中启动某个Service，此Service就是开机启动的。